Rectification by precooling and dividing the feed gas into partial streams

ABSTRACT

Improved rectification of a feed gas is achieved by precooling and dividing the precooled feed gas into two or more partial streams that are then introduced at different levels in the rectification zone.

United States Patent 1 1 3,631,683

[72] Inventors Helner Tanz [56] ReierenoesCited Doernisheim; UNITEDSTATES PATENTS Otto Kaiser, Rodenbach, both of Germany [21] PP No792,589 1,968,518 7/1934 Fraser 62/29 2,287,137 6/1942 Ross.... 62/29[22] F1led Jan. 21, 1969 2,327,459 8/1943 R1ce 62/29 [45] Patented Jan.4, 1972 2,517,134 8/1950 R1ce 62/29 [73] Assignee Messer Grlesheim GmbH2,527,623 10/1950 Fausek 62/29 2 918 s 1 12 1 59 F 62 40 [32] 1968 3 5438 2 1370 clrSt f d 152/29 [33] Germany ,52 1 raw or [31] P 16 01 257.0Primary Examiner-Norman Yudkoff Assistant Examiner-Arthur F. PurcellAt1orneyPaul W. Garbo [54] RECTIFICATION BY PRECOOLING AND 22 2 2. A 2 2DIVIDING THE FEED GAS INTO PARTIAL STREAMS 1 Claim, 2 Drawing Figs.

[52] US. Cl 62/28 ABSTRACT: Improved rectification of a feed gas isachieved [51] Int. Cl F25j l/00, by precooling and dividing theprecooled feed gas into two or F25j 5/00 more partial streams that arethen introduced at different [50] Field of Search 62/23, 24, levels inthe rectification zone.

*Q'VHH HI IH IIII RECTIFICATION BY PRECOOLING AND DIVIDING THE FEED GASINTO PARTIAL STREAMS BACKGROUND OF THE INVENTION This invention relatesto a process for improved rectification by precooling and dividing theprecooled feed gas mixture into partial streams of high-liquid andlow-liquid contents at different temperatures. More particularly, thisinvention relates to such rectification processes where the feed gasmixture is at a higher pressure than that of the rectifying column, andenters the column, after expansion, as a wet vapor.

It is known that rectification is accomplished more easily when the feedgas mixture, before entering the column, is divided into two partialstreams of different liquid contents. This is achieved by heating onestream with a source of heat, and cooling the other stream with a sourceof refrigeration. Thus, the first partial stream is a wet vapor oflow-liquid content and the second stream is a wet vapor of high-liquidcontent. The second partial stream is fed to the column a few traysabove the first one.

In such process, free energy is added to the feed gas mixture by meansof the aforesaid sources of heat and refrigeration.

This invention is an improvement of the process disclosed and claimed incopending Pat. application Ser. No. 775,402, filed Nov. 13, 1968, byOtto Kaiser. The process of said copending application carries out therectification of a divided feed gas, without the necessity of addingfree energy thereto, by passing in heat exchange relation an expandedpartial stream of the feed gas with another partial stream before thelatter is expanded.

SUMMARY OF THE INVENTION:

It is the object of this invention to carry out an improved rectifyingprocess with a divided feed gas, without the necessity of adding freeenergy thereto, in which process the difference between theliquid-to-vapor ratios of the partial streams is greater than hasheretofore been achieved.

A process was found for the rectification of a gas mixture, in which thefeed gas mixture is divided into two partial streams of different liquidcontents. The partial stream with the higher liquid content is fed tothe column a few trays above the tray where the partial stream oflow-liquid content is introduced. The characteristic feature of thisprocess is that all of the feed gas stream is first precooled with therefrigeration of a precooled partial stream thereof which has beenexpanded, the expanded partial stream is then fed into the column, andanother precooled partial stream is also expanded and fed, withoutgiving up its refrigeration, into the column a few trays above the firstpartial stream.

A slight improvement of this process can be achieved by further coolingall of the precooled second partial stream with the refrigerationproduced by expanding only the part of the further cooled precooledsecond stream remaining after a third partial stream has been dividedtherefrom. The expanded remainder of the further cooled precooled secondstream, after transferring its refrigeration, is introduced into thecolumn a few trays above the tray where the first partial stream entersthe column, while the third partial stream is also expanded and fed,without giving up its refrigeration, into the column a few trays abovethe tray where the second partial stream enters the column.

In the description which follows, a two-component gas mixture is used toexplain the process in detail. Of course, the process is not limited totwo-component mixtures.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 shows a process diagram in which the feed gas is divided intothree anial streams.

DESCRIP'ITON OF PREFERRED EMBODIMENT:

According to this invention, the feed gas mixture 12, as shown in FIG.I, is precooled in heat exchanger 2 by a partial stream of the precooledfeed gas which has been expanded through expansion valve 1. Afterpassing through heat exchanger 2, the expanded first partial streamenters rectifying column 4 by way of line 3 as a wet vapor of relativelylowliquid content. The precooled second partial stream is then expandedthrough expansion valve 5 and introduced into rectifying column 4 byline 6 as a wet vapor of relatively high-liquid content, several traysabove the tray where the first partial stream enters the column.

FIG. 2 shows the process of this invention with a division of the feedgas mixture into three partial streams. The symbols used in FIG. 2 arethe same as used in FIG. 1. To begin with, the feed gas stream 12 isprecooled in heat exchanger 2 and divided into two partial streams. Theprecooled first stream is expanded to column pressure through expansionvalve 1, heated in heat exchanger 2, and fed to rectifying column 4through line 3 as a wet vapor of low-liquid content. The precooledsecond partial stream is further cooled in heat exchanger 8 and thenagain divided into two partial streams. One of these further cooledprecooled partial streams is expanded through expansion valve 7 tocolumn pressure and thereby cooled, then somewhat heated in heatexchanger 8 and fed to rectifying column 4 through line 9, a few traysabove the tray where the first partial stream is introduced. Theremaining or third partial stream is further cooled by expansion throughexpansion valve 10 to column pressure and introduced by line 11 intocolumn 4 as the coldest partial stream with the highest-liquid content.It is therefore fed to rectifying column 4, several trays higher thanthe trays where the two other partial streams enter the column.

As already mentioned, the process of this invention is an improvement ofthe process of copending application Ser. No. 775,402, in that thedifference between the liquid contents of the partial streams of the gasmixture fed to the rectifying column has been increased by thisinvention. Consequently, the intersecting points of the rectificationlines in the relevant McCabe-Thiele diagram are now further apart; inshort, rectification has been improved.

What is claimed is:

I. In the process for the rectification of a feed gas mixture atelevated pressure, the improvement which comprises precooling said feedgas and then dividing the precooled feed gas into two partial streams ofthe same composition, expanding one partial stream through an expansionvalve, passing the expanded partial stream in countercurrent heatexchange relation with said feed gas to effect the aforesaid precoolingthereof, then introducing said expanded partial stream as a wet vapor ofrelatively low-liquid content into a rectification zone, further coolingand then dividing the other partial stream to provide a further cooledthird partial stream, expanding the remainder of the further cooledother partial stream through an expansion valve and passing it incountercurrent heat exchange relation with said other partial stream toeffect the aforesaid further cooling thereof, then introducing theexpanded remainder of the further cooled other partial stream as a wetvapor of relatively high-liquid content into said rectification zone ata tray above the tray at which said wet vapor of relatively low-liquidcontent is introduced, and expanding said further cooled third partialstream through an expansion valve and introducing it into saidrectification zone at a tray above the tray at which said wet vapor ofrelatively high-liquid content is introduced.

